1. Field of the Invention
The present invention relates to a communication system having a telephonic function which is suitable for application with a facsimile system having a telephonic function and also a so-called auto-dialing function. This enables a user to automatically effect a series of processes ranging from designation of a receiving station to termination of subsequent transmission of a manuscript to a personal computer, having a telephonic function, for transmitting information via a telephone line.
2. 2. Description of the Prior Art
A facsimile system having an auto-dialing function and also a telephonic function normally incorporates a facsimile module including a modem unit (a conversion unit for modulating and demodulating carrier signals which are transmitted and received via a telephone line). The facsimile module further includes a key input unit designed for dialing, a DP (dial impulse) signal generating unit and a PB (push button) signal generating unit. The DP signal generating unit and the PB signal generating unit are controlled in accordance with selection signals generated by a selection signal generating unit incorporated into the facsimile module; and thus a PB signal or a DP signal is transmitted, depending on which is required, to reach a particular destination calling number.
A telephone module is also equipped with another key input unit and a selection signal generating unit. When utilizing the facsimile system as a telephone, the selection signal generating unit incorporated into the telephone module serves to control the DP signal generating unit or the PB signal generating unit.
The reason why the facsimile module and the telephone module are in overlap, being equipped with the key input unit and the selection signal generating unit respectively, lies in the purposes for permitting the use of only the telephone module in the case of stoppage of electric current and for preventing noises from entering the telephone line by electrically isolating the telephone module from other units.
In the prior art, therefore, the key input units and the selection signal generating units must be duplicated this leads to higher manufacturing cost.
In order to obviate the above-described problems, a "telephone-built-in facsimile system" disclosed in Japanese Patent Laid-Open Publication No. 65553/1987 is constructed in such a way that a key board of the facsimile system serves as dialing keys, and a change-over circuit supplies dialing signals directly to a telephone circuit when a control circuit is brought into a non-operative state (off state) under control of the control circuit of the facsimile system. There is not, however, disclosed definitive change-over means for electrically isolating the telephone module from the facsimile module. Hence, the means for sharing the key input unit and the selection signal generating unit, and for changing over these units to an isolated state as required has not yet been invented.